An easy visible mistake is a player set as starter AND as entering substitution. After entering subs there is the outgoing player listed in brackets. So, actually you shouldn't see these brackets after any starter. If it does, it means the same player is listed as starter, too. Example:
In this case Alsény Agogo Camara is set twice as starter and as entering sub. His namesake Alsény Cantona Camara was the starter, source and see team pic below:
Besides namesakes, another frequent mistake can be changing the order of incoming and outgoing substitute player, so the starter (and outgoing player) is set by mistake as entering player, too which creates also the brackets with the wrongly suposed to be exchanged player.
So, whenever you see such brackets after a starting player, you know there is a mistake.
